The
atmosphere of Saturn normally appears calm, but about once
per Saturn year — equal to about 30 Earth years — the giant world
is gripped by a titanic storm as spring comes to its northern
hemisphere. The current
monster Saturn storm erupted last Dec. 5.

"This disturbance in the northern hemisphere of Saturn
has created a gigantic, violent and complex eruption of bright
cloud material, which has spread to encircle the entire planet,"
said researcher Leigh Fletcher, a planetary scientist at the
University of Oxford in England.

It took less than a month for the storm to radically disrupt the
temperature, winds and composition of the atmosphere in an area
87,000 miles (140,000 kilometers) wide, between 20 and 50 degrees
north. [ Photos:
Rings and Moons of Saturn ]

This is only the sixth monstrous storm detected on Saturn since
1876. It is the first to be observed by an orbiter, NASA's
Cassini spacecraft, which used its radio and plasma wave science
instrument to first detect it.

It is also the first to be monitored in the thermal infrared,
using Cassini's Composite Infrared Spectrometer instrument and
the European Southern Observatory's Very Large Telescope in
Chile.

"Previous studies of these storms have only been able to use
reflected sunlight," Fletcher said, "but now, by observing
thermal infrared light for the first time, we can reveal hidden
regions of the atmosphere and measure the truly spectacular
changes in temperatures and winds associated with this event."

Researcher Glenn Orton at NASA's Jet Propulsion Laboratory in
Pasadena, Calif., said these new observations "show that the
storm had a major effect on the atmosphere, transporting energy
and material over great distances, modifying the atmospheric
winds — creating meandering jet streams and forming giant
vortices — and disrupting
Saturn's slow seasonal evolution."

Stormy Saturn clouds

The storm may have originated deep down in Saturn's water clouds.
There, just as hot air rises in a heated room, a huge mass of gas
"rather like a system of thunder clouds" could have punched
upwards through the ringed planet's normally serene upper
atmosphere, Fletcher explained.

This bright plume of clouds then interacted with circulating
winds moving east and west, triggering never-before-seen
anomalies described as "stratospheric beacons" — very strong
changes in temperature approximately 155 to 185 miles (250 to 300
kilometers) above the cloud tops of the lower atmosphere.

These beacons are invisible in reflected sunlight, but in thermal
infrared light they can outshine the emissions from the rest of
the planet. While Saturn's stratosphere is normally about 200
degrees below zero Fahrenheit (minus 130 degrees Celsius) at this
season, the beacons are warmer by about 25 to 35 degrees
Fahrenheit (15 to 20 C).

"The beacons have persisted from at least January 2 to the
present day ... in fact, the beacons have grown stronger,"
Fletcher told SPACE.com. "They're at least 30,000 kilometers
(18,600 miles) wide, and there was one on either side of the
central disturbance."

Anatomy of an extraterrestrial storm

When analyzing how these beacons developed, "the images show that
the stratosphere over the disturbance is cold, suggesting rising
air, but flanked by warmer regions to the east and west,"
Fletcher said. "What comes up must go down, so these beacons may
be formed by air subsiding and warming up in the stratosphere.

Astronomers are not sure if these hot spots are common features
in such storms. "The beacons are so new that we're uncertain what
their fate may be, but we'll be continuing to track them to see
how they evolve over the coming months," Fletcher said.

In addition, a new, cold oval vortex about 3,400 miles (5,500 km)
wide was born in the middle of the disturbance.

"We believe it's cold for the same reasons as Jupiter's Great Red
Spot," Fletcher said. "You have a central core of upwelling air,
which expands when it reaches the top of the troposphere [the
lowest portion of the atmosphere], and that expansion causes
cooling."

The turbulence of the storm causes temperature and pressure
differences, "and air tends to circulate around regions of
different pressure," he added."In most cases, this just causes a
jet stream to meander like a wave, but in this instance the flows
formed a spinning vortex, which might be analogous to the
formation of spinning weather systems on Earth.

"We didn't see anything like that in previous storms, but then
again, we didn't have the resolution or the infrared capabilities
to do so," Fletcher said. "I don't think we expected something
quite so complex or beautiful to emerge from this storm system,
and given that it's embedded in this turbulent weather system, we
can't say how long it might last."

Nevertheless, the researchers expect the aftermath of this storm
to influence Saturn's northern hemisphere for years to come.

"The cold vortex might be ephemeral in nature, but the
disturbance in general has had a dramatic effect already, moving
the atmosphere around and redistributing Saturn's energy and
composition," Fletcher said. "We are continuing to observe this
once-in-a-generation event."

The intense variations in heat emissions seen here in Saturn
could happen not just elsewhere in our solar system, but on alien
worlds. These findings show "that you need continuous monitoring,
rather than just snapshots, to really understand these
complicated atmospheres, both in our solar system and beyond,"
Fletcher said.

The scientists detail their findings online May 19 in the journal
Science.

Follow SPACE.com contributor Charles Q. Choi on Twitter @cqchoi. Visit
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